The present invention relates to the field of semiconductors, and in particular to a semiconductor arrangement having at least two integrated circuits (dies) arranged in a housing or a package and electrically connected to each other via bond conductors.
Bond conductors or bond wires have long been known in the fabrication of integrated circuits. In microelectronic construction and connection technology, bond conductors are commonly made of gold or a gold alloy. Alternatively, some bond conductors are made of aluminum.
Typically, bond conductors are used in an integrated circuit to connect contacts that extend outside a housing (also referred to as “pins”) to electrical contact regions (also referred to as “bond islands” or “pads”) disposed on a chip lying inside the housing. The bond conductor provides an electrical connection between the integrated circuit proper and the wiring substrate of an electronic circuit. The bond conductor extends between and electrically connects/couples the contact pads of the chip and the inner part of the external contact. The bond conductors may be coupled to the pad and the contact using either thermosonic bonding or ultrasonic bonding. After bonding, the integrated circuits are hermetically potted into a housing, preferably a plastic housing.
Bond conductors are also used for electrically connecting respective contact pads disposed on two or more dies in a housing. According to G. G. Harman, Wire Bonding in Microelectronics, McGraw-Hill, 1997, pages 1-10, pages 67 ff. and pages 203 ff., in the ball-wedge technique, the bond wire is bonded to the contact pad of a first integrated circuit using flamed-off sphere (also known as a “free-air ball” (FAB)), and at the other end is flattened into a wedge shape and connected to the contact pad of the second integrated circuit. However, disadvantageously, the ball-wedge technique exerts compressive loading (e.g., using ultrasonic techniques) on the second integrated circuit when the bond wire is flattened and pressed thereon. In order to reduce the compressive loading on the second integrated circuit, spherical intermediate elements made of electrically conductive material are provided to sit on the contact pad of the second integrated circuit. The second end of the bond conductor, flattened into a wedge shape, is pressed onto this spherical intermediate element. This intermediate element serves to relieve the pressure on the second integrated circuit as the bond wire is pressed thereon.
Prior art bond conductors may be made from materials such as copper and silver. However, these materials may tarnish (i.e., oxidize upon contact with air), for example, during the manufacturing process, thereby reducing the bonding capacity of the bond conductors. Therefore, bonding of, for example, copper bond conductors is often carried out using a shielding gas in order to prevent the oxidation of the copper. As a result, chip-to-chip bond conductors are generally made of gold, despite its inferior electrical and mechanical properties to that of copper and silver, since, unlike copper and silver, gold does not tarnish. However, disadvantageously, gold bond conductor increase manufacturing costs due to the high price of the material (i.e., gold). This becomes especially problematic where a large number (e.g., hundreds to thousands) of bond conductors are necessary in a semiconductor arrangement due to the increasingly high packing density inside housings.
Due to the high costs related to gold bond conductors, alternative techniques have been used to utilize other more favorable materials. In a first example, according to published U.S. Patent Application 2003/0113574 A1, gold-jacketed silver or palladium wires, as compared with pure gold wires, have been furnished to reduce costs. In a second example, German patent application DE 10 2005 011028 A1 discloses the use of copper-gold alloys in bond conductors. In comparison with pure gold, copper-gold alloys have a significantly greater hardness. However, this hardness is undesirable for bond wires because integrated circuits may be damaged by the pressing of the bond wire or bond conductor onto the contact pad of the integrated circuit. For example, gold-copper alloys on copper wires can cause cracking in the silicon chip of the integrated circuit when pressed against the contact pad, which may lead to the failure of the integrated circuit. In a third example, German patent application DE 10 2005 011028 A1 discloses a copper bond conductor containing a small quantity of gold in the surface thereof. This publication discloses that it is especially preferable to use a copper bond conductor having gold enriched surface. The quantity of gold used to enrich the surface corresponds to a jacketing of at most fifty nano-meters (50 nm) thick, if the gold were fashioned uniformly as a coating on the wire. However, similar to pure gold bond conductors, such gold-coated copper wires are relatively expensive to manufacture.
Therefore, there is a need in the art for a semiconductor arrangement having a bond conductor that reduces associated manufacturing costs.